Lubricating oil composition

ABSTRACT

A lubricating oil composition is provided containing one or more hydrocarbyl-substituted aromatic lubricant base oils in combination with (a) one or more phenyl-naphthylamines, and (b) one or more diphenyl amines, where said lubricating oil composition comprises one or more additional lubricant base oils comprising polyalphaolefins and/or Fischer-Tropsch derived base oils. Further, the present invention relates to the use of the lubricating oil composition for lubricating a rotary air compressor.

FIELD OF THE INVENTION

The present invention relates to lubricating oil compositions, more specifically to lubricating oil compositions for lubricating rotary air compressors.

BACKGROUND OF THE INVENTION

The lubrication of compressors, in particular rotary air compressors, can expose the lubricant to high temperature conditions. Lubricating oil compositions for use in such compressors have to meet a combination of requirements in order to satisfactorily lubricate each component.

In order that the need for oil changes can be minimised in such compressors, i.e. in order that the oil drain interval is favorable, such lubricating oil compositions must exhibit not only good deposit control, but also good thermal and oxidative stability.

WO-A-01/64820 describes a lubricating oil composition comprising a lubricating basestock which comprises a blend of (A) at least one polyalkylene glycol (PAG) and (B) at least one alkyl aromatic compound. It is indicated that such lubricating oil composition can be used as a positive displacement compressor lubricant. WO-A-01/64820 exemplifies lubricating oil compositions comprising a PAG in combination with an alkyl naphthalene and various antioxidants.

EP-A-0387979 discloses specific alkyl-substituted diphenylamines as antioxidants, i.e. p,p′-dinonyldiphenylamines. EP-A-0387979 further discusses the use of such antioxidants in lubricating oil compositions comprising mineral oil having an aromatic content of 30% by weight or below and/or synthetic oil containing no aromatic rings in its structural units.

That is to say, EP-A-0387979 teaches away from the use of said antioxidants with aromatic lubricant base oils.

EP-A-0387979 discloses a composition comprising a p,p′-dinonyldiphenylamine, N-p-dodecylphenyl-α-naphthylamine, and, as base oil, either a purified mineral oil having an aromatic content of 7% by weight or a poly-α-olefin oil. However, there is no disclosure in EP-A-0387979 of the specific lubricating oil compositions of the present invention.

Table 2 of EP-A-0387979 shows a composition comprising p,p′-branched dinonyldiphenylamine (Ex. 5) and N-p-branched dodecylphenyl-α-naphthylamine in such purified mineral oil which has an oxidation-inhibiting performance (according to ASTM D2272) of 2154 minutes. Furthermore, Comparative Example 4 in such Table describes a composition comprising p,p′-branched dioctyldiphenylamine and N-p-branched octylphenyl-α-naphthylamine in such purified mineral oil which has an oxidation-inhibiting performance (according to ASTM D2272) of 2127 minutes.

U.S. Pat No. 6,180,575 describes lubricating oil compositions which may be used in the lubrication of bearings, gears and in other industrial applications such as in wet clutch systems, cooling gear boxes and rotary screw compressors.

Such lubricating oil compositions comprise a base fluid which comprises at least 50 wt. % of a hydrocarbon base fluid; and an additive combination comprising:

-   (1) an adduct of a substituted triazole and a hydrocarbon amine     phosphate in an amount below about 5 wt. % of the total composition     and -   (2) a tri-hydrocarbyl phosphate in an amount up to 5 wt. % of the     total composition,     wherein the ratio of the tri-hydrocarbyl phosphate to the adduct is     between about 2:1 to about 5:1.

U.S. Pat No. 6,180,575 lists a number of conventional additives including viscosity index improvers, antioxidants, anti-wear additives and corrosion inhibitors which may also be present in such lubricating oil compositions. It is of note that whilst U.S. Pat No. 6,180,575 lists a number of different kinds of antioxidants in the description thereof, the antioxidants are not a critical feature of the Examples in U.S. Pat No. 6,180,575 and they are not described in detail therein. Thus, Example 3 of U.S. Pat No. 6,180,575 is said to be an ISO grade 32 oil comprising 20.00% wt. C14 alkyl naphthalene, 76.78% wt. of a mixture of PAO and 0.75% wt. of an amine antioxidant. Such oil is indicated to have a RBOT value of 1750 minutes according to ASTM D2272.

However, there remains the need to develop lubricating oil compositions having improved performance in order that the oil drain interval can be increased still further.

SUMMARY OF THE INVENTION

A lubricating oil composition is provided, comprising one or more hydrocarbyl-substituted aromatic lubricant base oils in combination with:

(a) one or more phenyl-naphthylamines, and

(b) one or more diphenylamines,

wherein said lubricating oil composition comprises one or more additional lubricant base oils comprising polyalphaolefins and/or Fischer-Tropsch derived base oils.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, lubricating oil compositions have been found which not only exhibit good deposit control, but which also exhibit excellent oxidative and thermal stability.

The lubricating oil composition according to the present invention comprises one or more hydrocarbyl-substituted aromatic lubricant base oils in combination with (a) one or more phenyl-naphthylamines and (b) one or more diphenylamines, wherein said lubricating oil composition comprises one or more additional lubricant base oils comprising polyalphaolefins and/or Fischer-Tropsch derived base oils.

The lubricating composition according to the present invention can comprise a single compound or a mixture of compounds for each of components (a) and (b).

The one or more phenyl-naphthylamines (a) which are used in the present invention, can be either substituted or non-substituted, or a mixture of both. The one or more phenyl-naphthylamines can be used as such or in the form of a salt. Examples of such phenyl-naphthylamines are phenyl-alpha-naphthylamines and phenyl-beta-naphthylamines. The phenyl-naphthylamine preferably is a phenyl-alpha-naphthylamine.

A preferred substituted phenyl-naphthylamine is a mono-alkylated phenyl-alpha-naphthylamine.

Examples of phenyl-naphthylamines that may be conveniently used include octylphenyl-beta-naphthylamine, t-octylphenyl-alpha-naphthylamine, phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, phenyl-beta-naphthylamine, p-octylphenyl-alpha-naphthylamine, 4-octylphenyl-1-octyl-beta-naphthylamine, n-t-dodecylphenyl-1-naphthylamine, N-hexylphenyl-2-naphthylamine. A particularly preferred phenyl-alpha-naphthylamine is a monooctylated phenyl alpha-naphthylamine.

Another preferred phenyl-naphthylamine is a non-substituted phenyl-alpha-naphthylamine.

Examples of commercially available phenyl-naphthylamines that may be conveniently used in the lubricating oil composition of the present invention include that available from Ciba Specialty Chemicals under the trade designation “IRGANOX L-06”.

The lubricating oil composition according to the present invention further comprises one or more diphenylamines (b). The one or more diphenylamines can be substituted or non-substituted. It is preferred to use a hydrocarbyl-substituted diphenylamine, more preferably an alkyl-substituted diphenylamine. A preferred diphenylamine is 4,4′-dialkyl diphenylamine. The alkyl group preferably contains in the range of from 2 to 15 carbon atoms, more preferably in the range of from 3 to 12 carbon atoms. Preferred diphenylamines include dialkyldiphenylamines such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine.

Examples of commercially available diphenylamines that may be conveniently used in the lubricating oil composition of the present invention include that available from Ciba Specialty Chemicals under the trade designation “IRGANOX L-57”.

The one or more hydrocarbyl-substituted aromatic lubricant base oils present in the lubricating oil composition of the present invention are preferably alkylated aromatic lubricant base oils, more preferably alkylated aromatic lubricant base oils selected from one or more of alkylated naphthalenes, alkylated benzenes, alkylated diphenyl compounds and alkylated diphenyl methanes. Such base oils are described in U.S. Pat No. 6,180,575 and may be conveniently prepared by the methods described therein. Different suitable base oils can have different lubricating viscosity. The one or more hydrocarbyl-substituted aromatic lubricant base oils essentially consist of compounds which only contain hydrogen and carbon. A limited amount of contaminants such as sulphur containing compounds may be present therein. Preferably, more than 80% wt of the one or more hydrocarbyl-substituted aromatic lubricant base oils consists of compounds consisting of hydrogen and carbon only, more preferably more than 90% wt.

Alkylated naphthalenes are preferred hydrocarbyl-substituted aromatic lubricant base oils for use in the lubricating oil compositions of the present invention. Said alkylated naphthalenes may be mono-, di-, tri or tetra-alkyl substituted naphthalenes such as those described in U.S. Pat. No. 5,602,086, WO-A-03/048275 and WO-A-03/048276.

The lubricating oil composition of the present invention comprises one or more additional lubricant base oils comprising polyalphaolefins and/or Fischer-Tropsch derived base oils.

As described in U.S. Pat No. 6,180,575 and U.S. Pat. No. 5,602,086, polyalphaolefins and their manufacture are well known in the art. Preferred polyalphaolefins that may be used in lubricating oil compositions of the present invention may be derived from C₂ to C₃₂ alpha olefins. Particularly preferred feedstocks for said polyalphaolefins are 1-octene, 1-decene, 1-dodecene and 1-tetradecene. Preferably, polyalphaolefins that may be conveniently used in the lubricating oil compositions of the present invention have a kinematic viscosity at 100° C. in the range of from 3 to 300 mm²/s, more preferably in the range of from 4 to 100 mm²/s.

Fischer-Tropsch derived base oils which may be conveniently used as the one or more additional base oils in the lubricating oil composition of the present invention include, for example, the Fischer-Tropsch derived base oils disclosed in EP-A-776959, EP-A-668342, WO-A-97/21788, WO-A-00/15736, WO-A-00/14188, WO-A-00/14187, WO-A-00/14183, WO-A-00/14179, WO-A-00/08115, WO-A-99/41332, EP-A-1029029, WO-A-01/18156 and WO-A-01/57166.

In one embodiment of the present invention, said one or more additional lubricant base oils may further comprise mineral and/or other synthetic lubricant base oils.

Such mineral lubricant base oils include liquid petroleum oils and solvent treated or acid treated mineral lubricating oils of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrocracking and hydrofinishing processes and/or dewaxing.

Naphthenic base oils have low viscosity index (VI) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content and are used mainly for lubricants in which colour and colour stability are important, and VI and oxidation stability are of secondary importance.

Paraffinic base oils have higher VI (generally >95) and a high pour point. Said base oils are produced from feedstocks rich in paraffins, and are used for lubricants in which VI and oxidation stability are important.

Synthetic processes enable molecules to be built from simpler substances or to have their structures modified to give the precise properties required.

Other synthetic lubricant base oils which may be present in the one or more additional lubricant base oils include hydrocarbon oils such as polyalkylene glycols (PAGs), polyisobutylenes (PIBs) dibasic acids esters, polyol esters and other complex esters, and dewaxed waxy raffinate. Synthetic hydrocarbon base oils sold by the Shell Group under the designation “XHVI” (trade mark) may be conveniently used.

Optional additional lubricant base oils are preferably constituted from mineral oils and/or other synthetic base oils which contain more than 80% wt of saturates, more preferably more than 90% wt., as measured according to ASTM D2007.

It is further preferred that said optional additional lubricant base oils contain less than 1.0 wt. %, more preferably less than 0.1 wt. % of sulphur, calculated as elemental sulphur and measured according to ASTM D2622, ASTM D4294, ASTM D4927 or ASTM D3120.

Preferably, the viscosity index of said optional additional lubricant base oils is more than 80, more preferably more than 120, as measured according to ASTM D2270.

Preferably, the lubricating oil composition of the present invention has a kinematic viscosity in the range of from 32 to 150 mm²/s at 40° C., more preferably in the range of from 32 to 100 mm²/s, and most preferably in the range of from 32 to 78 mm²/s.

The amount of the additives (a) and (b) present in the lubricating oil composition of the present invention, depends on the specific compounds used therein.

The lubricating oil composition of the present invention preferably comprises a total amount in the range of from 0.1 to 5.0% by weight, more preferably in the range of from 0.2 to 2.0% by weight of said one or more phenyl-naphthylamines, based on the total weight of the lubricating oil composition.

The lubricating oil composition of the present invention preferably comprises a total amount in the range of from 0.1 to 5.0% by weight, more preferably in the range of from 0.2 to 2.0% by weight, of said one or more diphenylamines, based on total weight of the lubricating oil composition.

The hydrocarbyl-substituted aromatic lubricant base oils are preferably present in the lubricating oil composition of the present invention in a total amount in the range of from 0.1 to 30% by weight, more preferably in the range of from 1 to 20% by weight, based on the total weight of the lubricating oil composition.

The one or more hydrocarbyl-substituted aromatic lubricant base oils preferably comprise less than 60 wt. % of the total lubricant base oil in the lubricating oil composition of the present invention, more preferably less than 25 wt. % of the total lubricant base oil and most preferably in the range of from 1 to 25 wt. % of the total weight of lubricant base oil, wherein the total weight of lubricant base oil is the total weight of the one or more hydrocarbyl-substituted aromatic lubricant base oils and the one or more additional lubricant base oils.

In a preferred embodiment of the present invention the one or more phenyl-naphthylamines (a) and the one or more diphenylamines (b) are present in the lubricating oil composition of the present invention in a weight ratio in the range of from 1:3 to 3:1, more preferably in the range of from 1:2 to 1:1.

It is preferred that the lubricating oil composition according to the present invention contains no substantial amount of phenolic antioxidant. The amount of phenolic antioxidant present preferably is less than 1% by weight, more preferably less than 0.5% by weight, even more preferably less than 0.1% by weight, and most preferably 0% by weight, based on total amount of the lubricating oil composition.

The lubricating oil composition of the present invention can further comprise additives such as extreme pressure additives, anti-wear additives, metal passivators, corrosion inhibitors, foam inhibitors and/or demulsifiers.

Anti-wear additives that may be conveniently used include zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates, molybdenum-containing compounds, boron-containing compounds and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof. Said anti-wear additives may each be conveniently added to the lubricating oil composition of the present invention in an amount in the range of from 0.1 to 3.0 wt. %, based on the total weight of lubricating oil composition.

Examples of such molybdenum-containing compounds may conveniently include molybdenum dithiocarbamates, trinuclear molybdenum compounds, for example as described in WO-A-98/26030, sulphides of molybdenum and molybdenum dithiophosphate.

Boron-containing compounds that may be conveniently used include borate esters, borated fatty amines, borated epoxides, alkali metal (or mixed alkali metal or alkaline earth metal) borates and borated overbased metal salts.

Compounds such as alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole-based compounds may be conveniently used in the lubricating oil composition of the present invention as corrosion inhibitors.

Compounds such as polysiloxanes, dimethyl polycyclohexane and polyacrylates may be conveniently used in the lubricating oil composition of the present invention as foam inhibitors.

The present invention further provides the use of the lubricating oil composition according to the present invention for lubricating a rotary air compressor.

The lubricating composition according to the present invention can be conveniently prepared by blending together the one or more phenyl-naphthylamines, the one or more diphenylamines, the one or more hydrocarbyl-substituted aromatic lubricant base oils and the one or more additional lubricant base oils comprising polyalphaolefins and/or Fischer-Tropsch derived base oils and, optionally, one or more additives as hereinbefore described.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the invention in any way.

EXAMPLES

Formulations were blended using the base oils and additives specified in Tables 1 and 2.

The phenyl-naphthylamine (a) used in the formulations of Tables 1 and 2 was that available from Ciba Specialty Chemicals under the trade designations “IRGANOX L-06”.

The diphenylamine (b) used in the formulations of Tables 1 and 2 was that available from Ciba Specialty Chemicals under the trade designation “IRGANOX L-57”.

The hydrocarbyl-substituted aromatic lubricant base oil used in the formulations of Tables 1 and 2 was the alkyl naphthalene available under the trade designation “SYNESSTIC 5” from ExxonMobil.

The PAO 40 base oil used in the formulations of Tables 1 and 2 was that available from Innovene under the trade designation “DURASYN 174”.

The PAO 8 base oil used in the formulations of Table 1 was that available from Innovene under the trade designation “DURASYN 168”.

The GTL 8 base oil used in the formulations of Table 2 was a Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of approx. 8 cSt (mm²s⁻¹). Said base oil may be conveniently manufactured by the process described in WO-A-02/070631.

Examples 1 and 2 are according to the present invention whilst the remaining Examples in Tables 1 and 2 are comparative in nature.

The formulations in Tables 1 and 2 were subjected to the Rotating Pressure Vessel Oxidation Test (RPVOT) (formerly known as the Rotating Bomb Oxidation Test (RBOT)) (ASTM D2272) in order to measure the oxidative stability thereof.

In addition, said formulations were also tested in a version of the Wolf Strip Test (formerly known as DIN 51392) performed according to the modifications set out below.

DIN 51392 formerly measured the tendency of engine oils to produce thermal/oxidative deposits using an inclined metal plate over which the test engine oils were pumped. The volume of oil, pumping rate, plate temperature and test duration specified in said test were 200 ml, 50 ml/hour, 250° C. and 12 hours, respectively.

In order to improve the test repeatability and to more closely simulate the type of thermal/oxidative stress that a lubricating oil composition would experience under full hydrodynamic film conditions in a compressor, the test conditions used in the Examples of Tables 1 and 2 were modified to an oil volume of 150 ml, a pumping rate of 50 ml/hour, a plate temperature of 205° C. and a test duration of 24 hours.

It is apparent from Tables 1 and 2 that the formulations in accordance with the present invention not only exhibit good deposit control but also display outstanding performance in the RPVOT. TABLE 1 Comp. Comp. Comp. Comp. Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Phenyl-naphthylamine 0.80 — — 0.80 — (a) (% wt.) Diphenylamine (b) 1.20 — — — 1.20 (% wt.) Hydrocarbyl substi- 10.00 — 10.00 10.00 10.00 tuted aromatic lubri- cant base oil (% wt.) PAO 40 (% wt.) 1.00 1.00 1.00 1.00 1.00 PAO 8 (% wt.) 87.00 99.00 89.00 88.20 87.80 TOTAL 100.00 100.00 100.00 100.00 100.00 RPVOT (ASTM D2272) 3990 20 58 2905 2829 (min) Wolf Strip Test 5 246 59 8 5 (modified DIN 51392) (205° C., 24 hours) (mg)

TABLE 2 Comp. Comp. Comp. Ex. 2 Ex. 5 Ex. 6 Ex. 7 Phenyl-naphthylamine (a) (% wt.) 0.80 — — 0.80 Diphenylamine (b) (% wt.) 1.20 — — — Hydrocarbyl substituted aromatic 10.00 — 10.00 10.00 lubricant base oil (% wt.) PAO 40 (% wt.) 1.00 1.00 1.00 1.00 GTL 8 (% wt.) 87.00 99.00 89.00 88.20 TOTAL 100.00 100.00 100.00 100.00 RPVOT (ASTM D2272) (min) 3716 35 85 3258 Wolf Strip Test (modified DIN <1 — — — 51392) (205° C., 24 hours) (mg) 

1. A lubricating oil composition comprising one or more hydrocarbyl-substituted aromatic lubricant base oils in combination with: (a) one or more phenyl-naphthylamines, and (b) one or more diphenylamines, wherein said lubricating oil composition comprises one or more additional lubricant base oils comprising polyalphaolefins and/or Fischer-Tropsch derived base oils.
 2. The lubricating oil composition of claim 1 wherein the one or more hydrocarbyl-substituted aromatic lubricant base oils are selected from one or more of alkylated naphthalenes, alkylated benzenes, alkylated diphenyl compounds, alkylated diphenyl methanes and mixtures thereof.
 3. The lubricating oil composition of claim 1 wherein the one or more hydrocarbyl-substituted aromatic lubricant base oils are one or more alkylated naphthalenes.
 4. The lubricating oil composition of claim 1 wherein the one or more phenyl-naphthylamines are phenyl-alpha-naphthylamines.
 5. The lubricating oil composition of claim 2 wherein the one or more phenyl-naphthylamines are phenyl-alpha-naphthylamines.
 6. The lubricating oil composition of claim 3 wherein the one or more phenyl-naphthylamines are phenyl-alpha-naphthylamines.
 7. The lubricating oil composition of claim 1 wherein the one or more diphenylamines are hydrocarbyl-substituted diphenylamines.
 8. The lubricating oil composition of claim 2 wherein the one or more diphenylamines are hydrocarbyl-substituted diphenylamines.
 9. The lubricating oil composition of claim 4 wherein the one or more diphenylamines are hydrocarbyl-substituted diphenylamines.
 10. The lubricating oil composition of claim 6 wherein the one or more diphenylamines are hydrocarbyl-substituted diphenylamines.
 11. The lubricating oil composition of claim 1 wherein said lubricating oil composition further comprises one or more additives selected from one or more extreme pressure additives, one or more anti-wear additives, one or more metal passivators, one or more corrosion inhibitors, one or more foam inhibitors, one or more demulsifiers, and one or more mixtures thereof.
 12. The lubricating oil composition of claim 1 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more phenyl-naphthylamines, based on the total weight of the lubricating oil composition.
 13. The lubricating oil composition of claim 3 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more phenyl-naphthylamines, based on the total weight of the lubricating oil composition.
 14. The lubricating oil composition of claim 7 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more phenyl-naphthylamines, based on the total weight of the lubricating oil composition.
 15. The lubricating oil composition of claim 1 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more diphenylamines, based on the total weight of the lubricating oil composition.
 16. The lubricating oil composition of claim 3 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more diphenylamines, based on the total weight of the lubricating oil composition.
 17. The lubricating oil composition of claim 7 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more diphenylamines, based on the total weight of the lubricating oil composition.
 18. The lubricating oil composition of claim 12 wherein said lubricating oil composition comprises a total amount in the range of from 0.1 to 5.0% by weight of said one or more diphenylamines, based on the total weight of the lubricating oil composition.
 19. The lubricating oil composition of claim 1 wherein said lubricating oil composition comprises a total amount in the range of 0.1 to 30% by weight of said one or more hydrocarbyl-substituted aromatic lubricant base oils, based on the total weight of the lubricating oil composition.
 20. The lubricating oil composition of claim 18 wherein said lubricating oil composition comprises a total amount in the range of 0.1 to 30% by weight of said one or more hydrocarbyl-substituted aromatic lubricant base oils, based on the total weight of the lubricating oil composition.
 21. The lubricating oil composition of claim 1 wherein the one or more phenyl-naphthylamines (a) and the one or more diphenylamines (b) are present in a weight ratio in the range of from 1:3 to 3:1.
 22. A method of lubricating a rotary air compressor wherein a lubricating oil composition of claim 1 is applied to at least a portion of said rotary air compressor. 